1. Field of the Invention
This invention relates to a two-speed resolver; and more particularly, to a resolver having both a fine and coarse sensing means and employing differential reduction techniques which utilize mechanical and electrical interconnection of the fine and coarse sensing means.
2. Description of the Prior Art
A resolver is an angle transducer which includes a rotor shaft containing two transformer-like windings disposed 90.degree. apart. The resolver also contains a pair of stationary transformer-like windings called the stator windings. In normal application the resolver shaft is directly coupled to the shaft which is to be instrumented in terms of angular position. The four windings are then connected in various arrangements to provide desired output for the given application. In utilizing a single resolver in an absolute positioning determining system with a shaft rotatable over multiple revolutions, an ambiguity exists from one revolution of the resolver to the next. That is, a single speed resolver can provide unique electrical signals relative to the position of a shaft within one revolution but cannot differentiate between revolutions. A single resolver directly coupled to a shaft can only provide positioning information over one particular revolution.
In order to provide information over a multiple number of revolutions and to know precisely which revolution is being monitored, a two-speed resolver system must be employed. In a two-speed resolver system a fine resolver is used for indicating the angular position of the instrumented shaft within the revolution being observed, and a coarse resolver is provided to determine which revolution is being checked.
A synchro or resolver is basically an angular position transducer which transmits information in the form of amplitude modulated sine wave signals. When excited, by a reference or carrier voltage of the form E sine .omega..sub.t, a typical resolver gives a two-phase signal as follows: EQU V.sub.s = (K.sub.s E sin .theta.) sin (.omega..sub.t + .psi..sub.s) EQU V.sub.c = (K.sub.c E cos .theta.) sin (.omega..sub.t + .psi..sub.c)
wherein:
.theta. is the mechanical input to the rotor PA1 K.sub.s and K.sub.c are the transmission factors of the resolver and are normally equal PA1 .psi..sub.s and .psi..sub.c are the phase shifts of the output signals and for a good resolver are practically zero.
Normally the desired angular positional information is carried by the ratio of two output signals V.sub.s and V.sub.c. Since the desired information out of the resolver is the sin .theta. and cos .theta., and the additional terms are in this sense surplusage, the resolver output is usually referred to for simplicity as sin .theta. and cos .theta., and this conventional terminology will be used.
Two-speed resolver systems are well known in the art. They have been widely used to provide electrical instrumentation for the determination of the position of a rotary shaft in applications where information is needed as to absolute shaft position over multiple revolutions. A typical two-speed resolver consists of two resolvers mechanically interconnected by a speed reducing means usually in the form of a gear reducer. The rotary shaft to be instrumented is generally coupled directy to a fine resolver, to mechanically provide input angle data representing the angular position of the shaft. The fine resolver directly coupled to the shaft is used to provide electrical signals over any given single revolution of the shaft indicating the angular orientation with a high degree of accuracy. By an appropriate gear reduction mechanism, angle theta, the angular position of the instrumented shaft, is mechanically transmitted to the input shaft of the second resolver, the coarse resolver. The coarse resolver provides electrical signals which indicate the total number of revolutions of the shaft to be instrumented. This combination of the fine resolver and coarse resolver thus provides electrical signals indicating the absolute position of the instrumented shaft over multiple revolutions.
For example, a typical two-speed resolver system may have a ratio between fine and coarse resolvers of 100:1. In such a system, the shaft to be instrumented can have a total rotation of 100 revolutions while the coarse resolver rotates only one revolution; thus, the resolver system provides non-ambiguous information for total shaft travel of 100 revolutions.
The principal difficulty in achieving large reduction ratios (of the order of magnitude of 100:1) in present day two-speed resolvers is with the gear system. In a normal system, a reduction of 5:1 is the largest practical ratio to obtain for a pair of gears. Thus, for a two-speed resolver having a 100:1 reduction ratio, as many as six gears and two additional bearing support systems may be required in order to achieve a reasonable size housing and the necessary precision. Since the gears are running at substantially different rates and substantial accuracy is required, gear wear can present a problem. In many cases cost of the precision gear train necessary to operate prior art two-speed resolver systems may exceed the cost of the two-speed resolvers themselves.